The present invention is concerned with a process for the conversion of a protected 4-hydroxy-2,6,6-trimethyl-2-cyclohexen-1-one (protected "phorenol") into the corresponding protected allylic epoxide, 4,8,8-trimethyl-1-oxaspiro2.5!octa-4-en-6-ol, using a reagent which has never previously been used for this purpose. Both the starting material and the end product are known valuable intermediates for the manufacture of carotenoids.
The method hitherto used for the aforementioned conversion (a "C.sub.1 -homologization") involved dimethylsulphonium methylide as the reagent see, for example, Pure & Appl. Chem. 51, 535-564 (1979), especially pages 546-547: 52+53.fwdarw.54; as well as Helv. Chim. Acta 63, 1451-1455 (1980), especially page 1452: 5.fwdarw.6!. This reagent is, however, troublesome to produce and yields as a byproduct the olfactorily annoying dimethyl sulphide, which are serious disadvantages.